The MPLS WG Archive

[Aditya@in.huawei.com]

Title: fault tolerant TCP implementation

Dear MPLS Gurus,
In the draft on ldp-FT (draft-ietf-mpls-ldp-ft-02.txt ) the authors write on Page 4, in section 2.2 that it  "Notoriously Hard

to provide a fault tolerant implementation of TCP"...My question is WHY ? .Why is it so difficult to recreate a TCP connection ( across a switchover

from Active Board to Standby Board ) if the connection is in ESTABLISHED state ?
Later they go on to say that  "This is an issue familiar to implementers of other TCP applications such as BGP".
If anyone could point me to any such related work,I would highly appreciate their help.
I guess that the close interaction of the TCP layer, socket layer and application complicates the problem? But HOW ?
If anybody is aware of any attempts to provide HotStandby for TCP,please do let me know......
Thanks in Advance,
Aditya
Extract from "draft-ietf-mpls-ldp-ft-02.txt" Section 2.2 Page 4
LDP and CR-LDP use TCP to provide reliable connections between LSRs over which to exchange protocol messages to distribute labels and to set up LSPs...... TCP enables LDP and CR-LDP to assume reliable transfer of protocol messages. This means that some of the messages do not need to be acknowledged (for example, Label Release). LDP and CR-LDP are defined such that if the TCP connection fails, the LSR should immediately tear down the LSPs associated with the session between the LDP peers, and release any labels and resources assigned to those LSPs. It is notoriously hard to provide a Fault Tolerant implementation of TCP. To do so might involve making copies of all data sent and received. This is an issue familiar to implementers of other TCP applications such as BGP.